The proposed investigations include the mapping by DNA/RNA hybridization of genes on human chromosomes and the determination of the mechanism responsible for amplification of the bobbed phenotype in Drosophila. Several studies, employing somatic cell hybridization, designed to determine the human chromosomes carrying specific genetic loci are proposed. Studies aimed at associating each of the autosomal linkage groups of the mouse with a specific pair of chromosomes will be continued. In addition, one experimental program will be concerned with the regulation of pyrimidine synthesis and of galactose metabolism in cultured human cells. Experiments, employing cultured mouse erythroid cells and human reticulocytes, directed towards identifying the factors which determine the transcription and processing of the messenger RNA for hemoglobin will be performed.